A hidden active galactic nucleus powering bright [O III] nebulae in a protocluster at z = 4.5 revealed by JWST

¹ Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército Libertador 441, 8370191 Santiago, Chile
² Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Santiago 7820436 Chile
³ Las Campanas Observatory, Carnegie Institution of Washington, Raúl Bitrán, 1200 La Serena, Chile
⁴ Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg, UMR 7550, 67000 Strasbourg, France
⁵ Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
⁶ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, 06000 Nice, France
⁷ Departamento de Astronomía, Facultad Ciencias Físicas y Matemáticas, Universidad de Concepción, Av. Esteban Iturra s/n Barrio Universitario, Casilla 160, Concepción, Chile
⁸ Chemistry Department, Sapienza University of Rome, P.le A. Moro, 00185 Rome, Italy
⁹ INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy
¹⁰ The University of Texas at Austin, 2515 Speedway Blvd Stop C1400, Austin, TX 78712 USA
¹¹ Cosmic Dawn Center (DAWN), Rådmandsgade 64, 2200 København N, Denmark
¹² Dipartimento di Fisica e Astronomia, Università di Padova, Vicolo dell’Osservatorio, 3, 35122 Padova, Italy
¹³ INAF Osservatorio Astronomico di Padova, vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹⁴ International Centre for Radio Astronomy Research (ICRAR), The University of Western Australia, M468, 35 Stirling Highway, Crawley, WA 6009 Australia
¹⁵ Centre for Astrophysics and Supercomputing, Swinburne Univ. of Technology, PO Box 218 Hawthorn, VIC 3122 Australia
¹⁶ ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Australia
¹⁷ Sterrenkundig Observatorium, Ghent University, Krijgslaan 281-S9, B-9000 Ghent, Belgium
¹⁸ Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT UK
¹⁹ Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo, Kashiwa, 277-8583 (Kavli IPMU WPI) Japan
²⁰ Institute of Astrophysics, Foundation for Research and Technology-Hellas (FORTH), Heraklion 70013 Greece
²¹ Chinese Academy of Sciences South America Center for Astronomy (CASSACA), National Astronomical Observatories, CAS, Beijing 100101 PR China
²² Caltech/IPAC, MS 314-6, 1200 E. California Blvd. Pasadena, CA 91125 USA
²³ Scuola Normale Superiore, Piazza dei Cavalieri 7, I-50126 Pisa, Italy
²⁴ Dipartimento di Fisica e Astronomia, Università di Firenze, via G. Sansone 1, 50019 Sesto Fiorentino, Firenze, Italy
²⁵ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, via Gobetti 93/3, 40129 Bologna, Italy
²⁶ Universidad Andrés Bello, Facultad de Ciencias Exactas, Departamento de Física, Instituto de Astrofísica, Fernandez Concha 700, Las Condes, Santiago, RM, Chile
²⁷ Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218 USA
²⁸ Instituto de Física y Astronomía, Universidad de Valparaíso, Avda. Gran Bretaña 1111, Valparaíso, Chile
²⁹ Hiroshima Astrophysical Science Center, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526 Japan
³⁰ Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH UK
³¹ Max-Planck-Institut für extraterrestrische Physik, Gießenbachstraße 1, 85748 Garching, Germany
³² Purple Mountain Observatory, Chinese Academy of Sciences, 10 Yuanhua Road, Nanjing 210023 China
³³ Center for Data-Driven Discovery, Kavli IPMU (WPI), UTIAS, The University of Tokyo, Kashiwa, Chiba 277-8583 Japan
³⁴ Department of Astronomy, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033 Japan
³⁵ Dipartimento di Fisica e Astronomia, Università di Bologna, via Gobetti 93/2, 40129 Bologna, Italy
³⁶ Dept. Fisica Teorica y del Cosmos, Universidad de Granada, Granada, Spain
³⁷ Instituto Universitario Carlos I de Física Teórica y Computacional, Universidad de Granada, E-18071 Granada, Spain
³⁸ I. Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany
³⁹ National Centre for Nuclear Research, ul. Pasteura 7, 02-093 Warsaw, Poland
⁴⁰ Department of Physics and Astronomy and George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University, 4242 TAMU, College Station, TX 77843-4242 USA
⁴¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, Bonn D-53121 Germany
⁴² University of California, Davis, 1 Shields Ave., Davis, CA 95616 USA
⁴³ Department of Astronomy and Joint Space-Science Institute, University of Maryland, College Park, MD 20742 USA
⁴⁴ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, 69120 Heidelberg, Germany
⁴⁵ Caltech Optical Observatories, California Institute of Technology, Pasadena, CA 91125 USA
⁴⁶ ESO Vitacura, Alonso de Córdova 3107, Vitacura, Casilla, 19001 Santiago de Chile, Chile

^⋆ Corresponding author; manuel.solimano@mail.udp.cl

Received: 17 July 2024
Accepted: 12 November 2024

Abstract

Galaxy protoclusters are sites of rapid growth, with a high density of massive galaxies driving elevated rates of star formation and accretion onto supermassive black holes. Here, we present new JWST/NIRSpec IFU observations of the J1000+0234 group at z = 4.54, a dense region of a protocluster hosting a massive, dusty star forming galaxy (DSFG). The new data reveal two extended, high-equivalent-width (EW₀ > 1000 Å) [O III] nebulae that appear at both sides of the DSFG along its minor axis (namely O3-N and O3-S). On one hand, the spectrum of O3-N shows a broad and blueshifted component with a full width at half maximum (FWHM) of ∼1300 km s⁻¹, suggesting an outflow origin. On the other hand, O3-S stretches over 8.6 kpc, and has a velocity gradient that spans 800 km s⁻¹, but shows no evidence of a broad component. However, both sources seem to be powered at least partially by an active galactic nucleus (AGN), so we classified them as extended emission-line regions (EELRs). The strongest evidence comes from the detection of the high-ionization [Ne V] λ 3427 line toward O3-N, which paired with the lack of hard X-rays implies an obscuring column density above the Compton-thick regime. The [Ne V] line is not detected in O3-S, but we measure a He IIλ 4687 /Hβ = 0.25, which is well above the expectation for star formation. Despite the remarkable alignment of O3-N and O3-S with two radio sources, we do not find evidence of shocks from a radio jet that could be powering the EELRs. We interpret this as O3-S being externally irradiated by the AGN, akin to the famous Hanny’s Voorwerp object in the local Universe. In addition, more classical line ratio diagnostics (e.g., [O III]/Hβ vs [N II]/Hα) put the DSFG itself in the AGN region of the diagrams, and therefore suggest it to be the most probable AGN host. These results showcase the ability of JWST to unveil obscured AGN at high redshifts.